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644c8c92ad
Without any form of coordination, any case where multiple allocations
from the same mempool are needed at a time to make forward progress can
deadlock under memory pressure.
This is the case for struct bio_post_read_ctx, as one can be allocated
to decrypt a Merkle tree page during fsverity_verify_bio(), which itself
is running from a post-read callback for a data bio which has its own
struct bio_post_read_ctx.
Fix this by freeing first bio_post_read_ctx before calling
fsverity_verify_bio(). This works because verity (if enabled) is always
the last post-read step.
This deadlock can be reproduced by trying to read from an encrypted
verity file after reducing NUM_PREALLOC_POST_READ_CTXS to 1 and patching
mempool_alloc() to pretend that pool->alloc() always fails.
Note that since NUM_PREALLOC_POST_READ_CTXS is actually 128, to actually
hit this bug in practice would require reading from lots of encrypted
verity files at the same time. But it's theoretically possible, as N
available objects doesn't guarantee forward progress when > N/2 threads
each need 2 objects at a time.
Fixes:
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.. | ||
acl.c | ||
acl.h | ||
checkpoint.c | ||
compress.c | ||
data.c | ||
debug.c | ||
dir.c | ||
extent_cache.c | ||
f2fs.h | ||
file.c | ||
gc.c | ||
gc.h | ||
hash.c | ||
inline.c | ||
inode.c | ||
Kconfig | ||
Makefile | ||
namei.c | ||
node.c | ||
node.h | ||
recovery.c | ||
segment.c | ||
segment.h | ||
shrinker.c | ||
super.c | ||
sysfs.c | ||
trace.c | ||
trace.h | ||
verity.c | ||
xattr.c | ||
xattr.h |