mm: fix exec activate_mm vs TLB shootdown and lazy tlb switching race

[linux/fpc-iii.git] / fs / xfs / xfs_filestream.c

/*
 * Copyright (c) 2006-2007 Silicon Graphics, Inc.
 * Copyright (c) 2014 Christoph Hellwig.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_sb.h"
#include "xfs_mount.h"
#include "xfs_defer.h"
#include "xfs_inode.h"
#include "xfs_bmap.h"
#include "xfs_bmap_util.h"
#include "xfs_alloc.h"
#include "xfs_mru_cache.h"
#include "xfs_filestream.h"
#include "xfs_trace.h"
#include "xfs_ag_resv.h"

struct xfs_fstrm_item {
        struct xfs_mru_cache_elem       mru;
        struct xfs_inode                *ip;
        xfs_agnumber_t                  ag; /* AG in use for this directory */
};

enum xfs_fstrm_alloc {
        XFS_PICK_USERDATA = 1,
        XFS_PICK_LOWSPACE = 2,
};

/*
 * Allocation group filestream associations are tracked with per-ag atomic
 * counters.  These counters allow xfs_filestream_pick_ag() to tell whether a
 * particular AG already has active filestreams associated with it. The mount
 * point's m_peraglock is used to protect these counters from per-ag array
 * re-allocation during a growfs operation.  When xfs_growfs_data_private() is
 * about to reallocate the array, it calls xfs_filestream_flush() with the
 * m_peraglock held in write mode.
 *
 * Since xfs_mru_cache_flush() guarantees that all the free functions for all
 * the cache elements have finished executing before it returns, it's safe for
 * the free functions to use the atomic counters without m_peraglock protection.
 * This allows the implementation of xfs_fstrm_free_func() to be agnostic about
 * whether it was called with the m_peraglock held in read mode, write mode or
 * not held at all.  The race condition this addresses is the following:
 *
 *  - The work queue scheduler fires and pulls a filestream directory cache
 *    element off the LRU end of the cache for deletion, then gets pre-empted.
 *  - A growfs operation grabs the m_peraglock in write mode, flushes all the
 *    remaining items from the cache and reallocates the mount point's per-ag
 *    array, resetting all the counters to zero.
 *  - The work queue thread resumes and calls the free function for the element
 *    it started cleaning up earlier.  In the process it decrements the
 *    filestreams counter for an AG that now has no references.
 *
 * With a shrinkfs feature, the above scenario could panic the system.
 *
 * All other uses of the following macros should be protected by either the
 * m_peraglock held in read mode, or the cache's internal locking exposed by the
 * interval between a call to xfs_mru_cache_lookup() and a call to
 * xfs_mru_cache_done().  In addition, the m_peraglock must be held in read mode
 * when new elements are added to the cache.
 *
 * Combined, these locking rules ensure that no associations will ever exist in
 * the cache that reference per-ag array elements that have since been
 * reallocated.
 */
int
xfs_filestream_peek_ag(
        xfs_mount_t     *mp,
        xfs_agnumber_t  agno)
{
        struct xfs_perag *pag;
        int             ret;

        pag = xfs_perag_get(mp, agno);
        ret = atomic_read(&pag->pagf_fstrms);
        xfs_perag_put(pag);
        return ret;
}

static int
xfs_filestream_get_ag(
        xfs_mount_t     *mp,
        xfs_agnumber_t  agno)
{
        struct xfs_perag *pag;
        int             ret;

        pag = xfs_perag_get(mp, agno);
        ret = atomic_inc_return(&pag->pagf_fstrms);
        xfs_perag_put(pag);
        return ret;
}

static void
xfs_filestream_put_ag(
        xfs_mount_t     *mp,
        xfs_agnumber_t  agno)
{
        struct xfs_perag *pag;

        pag = xfs_perag_get(mp, agno);
        atomic_dec(&pag->pagf_fstrms);
        xfs_perag_put(pag);
}

static void
xfs_fstrm_free_func(
        struct xfs_mru_cache_elem *mru)
{
        struct xfs_fstrm_item   *item =
                container_of(mru, struct xfs_fstrm_item, mru);

        xfs_filestream_put_ag(item->ip->i_mount, item->ag);

        trace_xfs_filestream_free(item->ip, item->ag);

        kmem_free(item);
}

/*
 * Scan the AGs starting at startag looking for an AG that isn't in use and has
 * at least minlen blocks free.
 */
static int
xfs_filestream_pick_ag(
        struct xfs_inode        *ip,
        xfs_agnumber_t          startag,
        xfs_agnumber_t          *agp,
        int                     flags,
        xfs_extlen_t            minlen)
{
        struct xfs_mount        *mp = ip->i_mount;
        struct xfs_fstrm_item   *item;
        struct xfs_perag        *pag;
        xfs_extlen_t            longest, free = 0, minfree, maxfree = 0;
        xfs_agnumber_t          ag, max_ag = NULLAGNUMBER;
        int                     err, trylock, nscan;

        ASSERT(S_ISDIR(VFS_I(ip)->i_mode));

        /* 2% of an AG's blocks must be free for it to be chosen. */
        minfree = mp->m_sb.sb_agblocks / 50;

        ag = startag;
        *agp = NULLAGNUMBER;

        /* For the first pass, don't sleep trying to init the per-AG. */
        trylock = XFS_ALLOC_FLAG_TRYLOCK;

        for (nscan = 0; 1; nscan++) {
                trace_xfs_filestream_scan(ip, ag);

                pag = xfs_perag_get(mp, ag);

                if (!pag->pagf_init) {
                        err = xfs_alloc_pagf_init(mp, NULL, ag, trylock);
                        if (err && !trylock) {
                                xfs_perag_put(pag);
                                return err;
                        }
                }

                /* Might fail sometimes during the 1st pass with trylock set. */
                if (!pag->pagf_init)
                        goto next_ag;

                /* Keep track of the AG with the most free blocks. */
                if (pag->pagf_freeblks > maxfree) {
                        maxfree = pag->pagf_freeblks;
                        max_ag = ag;
                }

                /*
                 * The AG reference count does two things: it enforces mutual
                 * exclusion when examining the suitability of an AG in this
                 * loop, and it guards against two filestreams being established
                 * in the same AG as each other.
                 */
                if (xfs_filestream_get_ag(mp, ag) > 1) {
                        xfs_filestream_put_ag(mp, ag);
                        goto next_ag;
                }

                longest = xfs_alloc_longest_free_extent(mp, pag,
                                xfs_alloc_min_freelist(mp, pag),
                                xfs_ag_resv_needed(pag, XFS_AG_RESV_NONE));
                if (((minlen && longest >= minlen) ||
                     (!minlen && pag->pagf_freeblks >= minfree)) &&
                    (!pag->pagf_metadata || !(flags & XFS_PICK_USERDATA) ||
                     (flags & XFS_PICK_LOWSPACE))) {

                        /* Break out, retaining the reference on the AG. */
                        free = pag->pagf_freeblks;
                        xfs_perag_put(pag);
                        *agp = ag;
                        break;
                }

                /* Drop the reference on this AG, it's not usable. */
                xfs_filestream_put_ag(mp, ag);
next_ag:
                xfs_perag_put(pag);
                /* Move to the next AG, wrapping to AG 0 if necessary. */
                if (++ag >= mp->m_sb.sb_agcount)
                        ag = 0;

                /* If a full pass of the AGs hasn't been done yet, continue. */
                if (ag != startag)
                        continue;

                /* Allow sleeping in xfs_alloc_pagf_init() on the 2nd pass. */
                if (trylock != 0) {
                        trylock = 0;
                        continue;
                }

                /* Finally, if lowspace wasn't set, set it for the 3rd pass. */
                if (!(flags & XFS_PICK_LOWSPACE)) {
                        flags |= XFS_PICK_LOWSPACE;
                        continue;
                }

                /*
                 * Take the AG with the most free space, regardless of whether
                 * it's already in use by another filestream.
                 */
                if (max_ag != NULLAGNUMBER) {
                        xfs_filestream_get_ag(mp, max_ag);
                        free = maxfree;
                        *agp = max_ag;
                        break;
                }

                /* take AG 0 if none matched */
                trace_xfs_filestream_pick(ip, *agp, free, nscan);
                *agp = 0;
                return 0;
        }

        trace_xfs_filestream_pick(ip, *agp, free, nscan);

        if (*agp == NULLAGNUMBER)
                return 0;

        err = -ENOMEM;
        item = kmem_alloc(sizeof(*item), KM_MAYFAIL);
        if (!item)
                goto out_put_ag;

        item->ag = *agp;
        item->ip = ip;

        err = xfs_mru_cache_insert(mp->m_filestream, ip->i_ino, &item->mru);
        if (err) {
                if (err == -EEXIST)
                        err = 0;
                goto out_free_item;
        }

        return 0;

out_free_item:
        kmem_free(item);
out_put_ag:
        xfs_filestream_put_ag(mp, *agp);
        return err;
}

static struct xfs_inode *
xfs_filestream_get_parent(
        struct xfs_inode        *ip)
{
        struct inode            *inode = VFS_I(ip), *dir = NULL;
        struct dentry           *dentry, *parent;

        dentry = d_find_alias(inode);
        if (!dentry)
                goto out;

        parent = dget_parent(dentry);
        if (!parent)
                goto out_dput;

        dir = igrab(d_inode(parent));
        dput(parent);

out_dput:
        dput(dentry);
out:
        return dir ? XFS_I(dir) : NULL;
}

/*
 * Find the right allocation group for a file, either by finding an
 * existing file stream or creating a new one.
 *
 * Returns NULLAGNUMBER in case of an error.
 */
xfs_agnumber_t
xfs_filestream_lookup_ag(
        struct xfs_inode        *ip)
{
        struct xfs_mount        *mp = ip->i_mount;
        struct xfs_inode        *pip = NULL;
        xfs_agnumber_t          startag, ag = NULLAGNUMBER;
        struct xfs_mru_cache_elem *mru;

        ASSERT(S_ISREG(VFS_I(ip)->i_mode));

        pip = xfs_filestream_get_parent(ip);
        if (!pip)
                return NULLAGNUMBER;

        mru = xfs_mru_cache_lookup(mp->m_filestream, pip->i_ino);
        if (mru) {
                ag = container_of(mru, struct xfs_fstrm_item, mru)->ag;
                xfs_mru_cache_done(mp->m_filestream);

                trace_xfs_filestream_lookup(ip, ag);
                goto out;
        }

        /*
         * Set the starting AG using the rotor for inode32, otherwise
         * use the directory inode's AG.
         */
        if (mp->m_flags & XFS_MOUNT_32BITINODES) {
                xfs_agnumber_t   rotorstep = xfs_rotorstep;
                startag = (mp->m_agfrotor / rotorstep) % mp->m_sb.sb_agcount;
                mp->m_agfrotor = (mp->m_agfrotor + 1) %
                                 (mp->m_sb.sb_agcount * rotorstep);
        } else
                startag = XFS_INO_TO_AGNO(mp, pip->i_ino);

        if (xfs_filestream_pick_ag(pip, startag, &ag, 0, 0))
                ag = NULLAGNUMBER;
out:
        IRELE(pip);
        return ag;
}

/*
 * Pick a new allocation group for the current file and its file stream.
 *
 * This is called when the allocator can't find a suitable extent in the
 * current AG, and we have to move the stream into a new AG with more space.
 */
int
xfs_filestream_new_ag(
        struct xfs_bmalloca     *ap,
        xfs_agnumber_t          *agp)
{
        struct xfs_inode        *ip = ap->ip, *pip;
        struct xfs_mount        *mp = ip->i_mount;
        xfs_extlen_t            minlen = ap->length;
        xfs_agnumber_t          startag = 0;
        int                     flags = 0;
        int                     err = 0;
        struct xfs_mru_cache_elem *mru;

        *agp = NULLAGNUMBER;

        pip = xfs_filestream_get_parent(ip);
        if (!pip)
                goto exit;

        mru = xfs_mru_cache_remove(mp->m_filestream, pip->i_ino);
        if (mru) {
                struct xfs_fstrm_item *item =
                        container_of(mru, struct xfs_fstrm_item, mru);
                startag = (item->ag + 1) % mp->m_sb.sb_agcount;
        }

        if (xfs_alloc_is_userdata(ap->datatype))
                flags |= XFS_PICK_USERDATA;
        if (ap->dfops->dop_low)
                flags |= XFS_PICK_LOWSPACE;

        err = xfs_filestream_pick_ag(pip, startag, agp, flags, minlen);

        /*
         * Only free the item here so we skip over the old AG earlier.
         */
        if (mru)
                xfs_fstrm_free_func(mru);

        IRELE(pip);
exit:
        if (*agp == NULLAGNUMBER)
                *agp = 0;
        return err;
}

void
xfs_filestream_deassociate(
        struct xfs_inode        *ip)
{
        xfs_mru_cache_delete(ip->i_mount->m_filestream, ip->i_ino);
}

int
xfs_filestream_mount(
        xfs_mount_t     *mp)
{
        /*
         * The filestream timer tunable is currently fixed within the range of
         * one second to four minutes, with five seconds being the default.  The
         * group count is somewhat arbitrary, but it'd be nice to adhere to the
         * timer tunable to within about 10 percent.  This requires at least 10
         * groups.
         */
        return xfs_mru_cache_create(&mp->m_filestream, xfs_fstrm_centisecs * 10,
                                    10, xfs_fstrm_free_func);
}

void
xfs_filestream_unmount(
        xfs_mount_t     *mp)
{
        xfs_mru_cache_destroy(mp->m_filestream);
}