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ufs: avoid grabbing ->truncate_mutex if possible

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tail unpacking is done in a wrong place; the deadlocks galore
is best dealt with by doing that in ->write_iter() (and switching
to iomap, while we are at it), but that's rather painful to
backport.  The trouble comes from grabbing pages that cover
the beginning of tail from inside of ufs_new_fragments(); ongoing
pageout of any of those is going to deadlock on ->truncate_mutex
with process that got around to extending the tail holding that
and waiting for page to get unlocked, while ->writepage() on
that page is waiting on ->truncate_mutex.

The thing is, we don't need ->truncate_mutex when the fragment
we are trying to map is within the tail - the damn thing is
allocated (tail can't contain holes).

Let's do a plain lookup and if the fragment is present, we can
just pretend that we'd won the race in almost all cases.  The
only exception is a fragment between the end of tail and the
end of block containing tail.

Protect ->i_lastfrag with ->meta_lock - read_seqlock_excl() is
sufficient.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2017-06-15 00:17:30 -04:00
parent 267309f394
commit 09bf4f5b6e
2 changed files with 26 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
fs/ufs/balloc.c
View File

@ -423,12 +423,12 @@ u64 ufs_new_fragments(struct inode *inode, void *p, u64 fragment,
if (result) {
ufs_clear_frags(inode, result + oldcount,
newcount - oldcount, locked_page != NULL);
*err = 0;
write_seqlock(&UFS_I(inode)->meta_lock);
ufs_cpu_to_data_ptr(sb, p, result);
write_sequnlock(&UFS_I(inode)->meta_lock);
*err = 0;
UFS_I(inode)->i_lastfrag =
max(UFS_I(inode)->i_lastfrag, fragment + count);
write_sequnlock(&UFS_I(inode)->meta_lock);
}
mutex_unlock(&UFS_SB(sb)->s_lock);
UFSD("EXIT, result %llu\n", (unsigned long long)result);
@ -441,8 +441,10 @@ u64 ufs_new_fragments(struct inode *inode, void *p, u64 fragment,
result = ufs_add_fragments(inode, tmp, oldcount, newcount);
if (result) {
*err = 0;
read_seqlock_excl(&UFS_I(inode)->meta_lock);
UFS_I(inode)->i_lastfrag = max(UFS_I(inode)->i_lastfrag,
fragment + count);
read_sequnlock_excl(&UFS_I(inode)->meta_lock);
ufs_clear_frags(inode, result + oldcount, newcount - oldcount,
locked_page != NULL);
mutex_unlock(&UFS_SB(sb)->s_lock);
@ -479,12 +481,12 @@ u64 ufs_new_fragments(struct inode *inode, void *p, u64 fragment,
ufs_change_blocknr(inode, fragment - oldcount, oldcount,
uspi->s_sbbase + tmp,
uspi->s_sbbase + result, locked_page);
*err = 0;
write_seqlock(&UFS_I(inode)->meta_lock);
ufs_cpu_to_data_ptr(sb, p, result);
write_sequnlock(&UFS_I(inode)->meta_lock);
*err = 0;
UFS_I(inode)->i_lastfrag = max(UFS_I(inode)->i_lastfrag,
fragment + count);
write_sequnlock(&UFS_I(inode)->meta_lock);
mutex_unlock(&UFS_SB(sb)->s_lock);
if (newcount < request)
ufs_free_fragments (inode, result + newcount, request - newcount);

26
fs/ufs/inode.c
View File

@ -401,13 +401,20 @@ static int ufs_getfrag_block(struct inode *inode, sector_t fragment, struct buff
u64 phys64 = 0;
unsigned frag = fragment & uspi->s_fpbmask;
if (!create) {
phys64 = ufs_frag_map(inode, offsets, depth);
if (phys64)
map_bh(bh_result, sb, phys64 + frag);
return 0;
}
phys64 = ufs_frag_map(inode, offsets, depth);
if (!create)
goto done;
if (phys64) {
if (fragment >= UFS_NDIR_FRAGMENT)
goto done;
read_seqlock_excl(&UFS_I(inode)->meta_lock);
if (fragment < UFS_I(inode)->i_lastfrag) {
read_sequnlock_excl(&UFS_I(inode)->meta_lock);
goto done;
}
read_sequnlock_excl(&UFS_I(inode)->meta_lock);
}
/* This code entered only while writing ....? */
mutex_lock(&UFS_I(inode)->truncate_mutex);
@ -451,6 +458,11 @@ static int ufs_getfrag_block(struct inode *inode, sector_t fragment, struct buff
}
mutex_unlock(&UFS_I(inode)->truncate_mutex);
return err;
done:
if (phys64)
map_bh(bh_result, sb, phys64 + frag);
return 0;
}
static int ufs_writepage(struct page *page, struct writeback_control *wbc)
@ -1161,7 +1173,9 @@ static void ufs_truncate_blocks(struct inode *inode)
free_full_branch(inode, block, i - UFS_IND_BLOCK + 1);
}
}
read_seqlock_excl(&ufsi->meta_lock);
ufsi->i_lastfrag = DIRECT_FRAGMENT;
read_sequnlock_excl(&ufsi->meta_lock);
mark_inode_dirty(inode);
mutex_unlock(&ufsi->truncate_mutex);
}