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f2fs: fix deadlock allocating bio_post_read_ctx from mempool
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: 95ae251fe8
("f2fs: add fs-verity support")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
parent
e8ce5749d7
commit
644c8c92ad
1 changed files with 19 additions and 6 deletions
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@ -204,19 +204,32 @@ static void f2fs_verity_work(struct work_struct *work)
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{
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struct bio_post_read_ctx *ctx =
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container_of(work, struct bio_post_read_ctx, work);
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struct bio *bio = ctx->bio;
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#ifdef CONFIG_F2FS_FS_COMPRESSION
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unsigned int enabled_steps = ctx->enabled_steps;
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#endif
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/*
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* fsverity_verify_bio() may call readpages() again, and while verity
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* will be disabled for this, decryption may still be needed, resulting
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* in another bio_post_read_ctx being allocated. So to prevent
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* deadlocks we need to release the current ctx to the mempool first.
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* This assumes that verity is the last post-read step.
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*/
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mempool_free(ctx, bio_post_read_ctx_pool);
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bio->bi_private = NULL;
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#ifdef CONFIG_F2FS_FS_COMPRESSION
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/* previous step is decompression */
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if (ctx->enabled_steps & (1 << STEP_DECOMPRESS)) {
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f2fs_verify_bio(ctx->bio);
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f2fs_release_read_bio(ctx->bio);
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if (enabled_steps & (1 << STEP_DECOMPRESS)) {
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f2fs_verify_bio(bio);
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f2fs_release_read_bio(bio);
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return;
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}
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#endif
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fsverity_verify_bio(ctx->bio);
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__f2fs_read_end_io(ctx->bio, false, false);
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fsverity_verify_bio(bio);
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__f2fs_read_end_io(bio, false, false);
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}
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static void f2fs_post_read_work(struct work_struct *work)
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